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Porcelain crabs resemble crabs, but are more closely related to squat lobsters and hermit crabs.[1]

Carcinisation (or carcinization) is an example of convergent evolution in which a crustacean evolves into a crab-like form from a non-crab-like form. The term was introduced into evolutionary biology by L. A. Borradaile, who described it as "one of the many attempts of Nature to evolve a crab".[2] Most carcinised crustaceans belong to the infraorder Anomura.

Definition of carcinised morphology[edit]

It was stated by Lancelot Alexander Borradaile in 1916 that:[3]

... carcinization … consists essentially in a reduction of the abdomen of a macrurous crustacean, together with a depression and broadening of its cephalothorax, so that the animal assumes the general habit of body of a crab

Keiler et al., 2017 defines a carcinised morphology as follows:[4]

  • "The carapace is flatter than it is broad and possesses lateral margins"
  • "The sternites are fused into a wide sternal plastron which possesses a distinct emargination on its posterior margin."
  • "The pleon is flattened and strongly bent, in dorsal view completely hiding the tergites of the fourth pleonal segment, and partially or completely covers the plastron"


Carcinisation is believed to have occurred independently in at least five groups of decapod crustaceans:[4]

The extinct probable crustacean order Cyclida are also noted to "strikingly resemble crabs", and probably had a similar ecology.[11][12]

King crabs[edit]

The example of king crabs (family Lithodidae) evolving from hermit crabs has been particularly well studied, and evidence in their biology supports this theory. For example, most hermit crabs are asymmetrical, so that they fit well into spiral snail shells; the abdomens of king crabs, even though they do not use snail shells for shelter, are also asymmetrical.[13][14][15][16]


An exceptional form of carcinisation, termed "hypercarcinisation", is seen in the porcelain crab Allopetrolisthes spinifrons. In addition to the shortened body form, A. spinifrons also shows similar sexual dimorphism to that seen in true crabs, where males have a shorter pleon than females.[17]


Some crab shaped species have evolved away from the crab form in a process known as decarcinisation.[18]

See also[edit]


  1. ^ Baeza, J. Antonio (2016-03-10). "Molecular phylogeny of porcelain crabs (Porcellanidae: Petrolisthes and allies) from the south eastern Pacific: the genera Allopetrolisthes and Liopetrolisthes are not natural entities". PeerJ. 4: e1805. doi:10.7717/peerj.1805. ISSN 2167-8359. PMC 4793318. PMID 26989636.
  2. ^ Patsy A. McLaughlin; Rafael Lemaitre (1997). "Carcinization in the Anomura – fact or fiction? I. Evidence from adult morphology". Contributions to Zoology. 67 (2): 79–123. doi:10.1163/18759866-06702001. PDF Archived 2012-04-02 at the Wayback Machine
  3. ^ Borradaile, L.A. (1916). "Crustacea. Part II. Porcellanopagurus: an instance of carcinization". British Antarctic ("Terra Nova") Expedition, 1910–1913. Natural History Report. Zoology. British Museum. 3 (3): 111–126. OCLC 1027015098.
  4. ^ a b Keiler, Jonas; Wirkner, Christian S.; Richter, Stefan (2017-05-01). "One hundred years of carcinization – the evolution of the crab-like habitus in Anomura (Arthropoda: Crustacea)". Biological Journal of the Linnean Society. 121 (1): 200–222. doi:10.1093/biolinnean/blw031. ISSN 0024-4066.
  5. ^ Jonas Keiler; Stefan Richter; Christian S. Wirkner (2013). "Evolutionary morphology of the hemolymph vascular system in hermit and king crabs (Crustacea: Decapoda: Anomala)". Journal of Morphology. 274 (7): 759–778. doi:10.1002/jmor.20133. PMID 23508935. S2CID 24458262.
  6. ^ Jonas Keiler; Stefan Richter; Christian S. Wirkner (2015). "The anatomy of the king crab Hapalogaster mertensii Brandt, 1850 (Anomura: Paguroidea: Hapalogastridae) – new insights into the evolutionary transformation of hermit crabs into king crabs". Contributions to Zoology. 84 (2): 149–165. doi:10.1163/18759866-08402004.
  7. ^ Jonas Keiler; Stefan Richter; Christian S. Wirkner (2014). "Evolutionary morphology of the organ systems in squat lobsters and porcelain crabs (Crustacea: Decapoda: Anomala): an insight into carcinization". Journal of Morphology. 276 (1): 1–21. doi:10.1002/jmor.20311. PMID 25156549. S2CID 26260996.
  8. ^ Jonas Keiler; Stefan Richter; Christian S. Wirkner (2016). "Revealing their innermost secrets: an evolutionary perspective on the disparity of the organ systems in anomuran crabs (Crustacea: Decapoda: Anomura)". Contributions to Zoology. 85 (4): 361–386. doi:10.1163/18759866-08504001.
  9. ^ "Remarkable new true crab-like hermit discovered". Florida Museum. University of Florida. 13 December 2013. Archived from the original on October 25, 2020. Retrieved December 9, 2020.
  10. ^ C. L. Morrison; A. W. Harvey; S. Lavery; K. Tieu; Y. Huang; C. W. Cunningham (2001). "Mitochondrial gene rearrangements confirm the parallel evolution of the crab-like form" (PDF). Proceedings of the Royal Society B: Biological Sciences. 269 (1489): 345–350. doi:10.1098/rspb.2001.1886. PMC 1690904. PMID 11886621. Archived (PDF) from the original on 2010-06-10. Retrieved 2010-03-26.
  11. ^ Günter Schweigert (2007). "Juracyclus posidoniae n. gen. and sp., the first cycloid arthropod from the Jurassic" (PDF). Journal of Paleontology. 81 (1): 213–215. CiteSeerX doi:10.1666/0022-3360(2007)81[213:JPNGAS]2.0.CO;2. S2CID 131620349. Archived (PDF) from the original on 2018-07-21. Retrieved 2020-08-30.
  12. ^ Castro, Peter; Davie, Peter; Guinot, Danièle; Schram, Frederick, eds. (2015-01-01), "Introduction to Brachyura", Treatise on Zoology – Anatomy, Taxonomy, Biology. The Crustacea, Volume 9 Part C (2 Vols), BRILL: 3–9, doi:10.1163/9789004190832_003, ISBN 978-90-04-19083-2, retrieved 2021-11-04
  13. ^ C. W. Cunningham; N. W. Blackstone; L. W. Buss (1992). "Evolution of king crabs from hermit crab ancestors". Nature. 355 (6360): 539–542. Bibcode:1992Natur.355..539C. doi:10.1038/355539a0. PMID 1741031. S2CID 4257029.
  14. ^ Patsy A. McLaughlin; Rafael Lemaitre; Christopher C. Tudge (2004). "Carcinization in the Anomura – fact or fiction? II. Evidence from larval, megalopal and early juvenile morphology". Contributions to Zoology. 73 (3): 165–205. doi:10.1163/18759866-07303001.
  15. ^ Ling Ming Tsang; Tin-Yam Chan; Shane T. Ahyong; Ka Hou Chu (2011). "Hermit to king, or hermit to all: multiple transitions to crab-like forms from hermit crab ancestors". Systematic Biology. 60 (5): 616–629. doi:10.1093/sysbio/syr063. PMID 21835822.
  16. ^ Rafael Lemaitre; Patsy A. McLaughlin (2009). "Recent advances and conflicts in concepts of anomuran phylogeny (Crustacea: Malacostraca)" (PDF). Arthropod Systematics & Phylogeny. 67 (2): 119–135. Archived from the original (PDF) on 2016-08-03. Retrieved 2011-11-19.
  17. ^ Alexandra Hiller; Carlos Antonio Viviana; Bernd Werding (2010). "Hypercarcinisation: an evolutionary novelty in the commensal porcellanid Allopetrolisthes spinifrons (Crustacea: Decapoda: Porcellanidae)" (PDF). Nauplius. 18 (1): 95–102. Archived from the original (PDF) on 2012-04-25.
  18. ^ Wolfe, Joanna M; Luque, Javier; Bracken-Grissom, Heather D (9 March 2021). "How to become a crab: Phenotypic constraints on a recurring body plan". BioEssays. 43 (5). doi:10.1002/bies.202100020. PMID 33751651. S2CID 232325601. Retrieved 8 November 2022.